当从底层 InputStream 解析时，Jackson 如何处理流结束读取（例如 -1、EOF）

Question

I have an ObjectReader parsing Json input from an underlying socket InputStream as follows:

jsonInput.readValue(handlerSocket.getInputStream());

, where jsonInput is the ObjectReader object.

I had configured jsonInput to parse to a particular type via the default readFor(Class<?>) method provided by the parent ObjectMapper . At the end of execution, part of the shutdown sequence involves shutting down the socket input ie calling handlerSocket.shutdownInput() and according to the Socket API Javadocs regarding shutdownInput() :

Places the input stream for this socket at "end of stream". Any data sent to the input stream side of the socket is acknowledged and then silently discarded. If you read from a socket input stream after invoking this method on the socket, the stream's available method will return 0, and its read methods will return -1 (end of stream).

I would have referred to the Jackson documentation regarding this particular implementation of readValue() but there is little to no relevant information to go on. My question is then how does Jackson treat end-of-stream type scenarios such as this one? Will null be returned? A parsing exception? Would appreciate your insights.

Answer 1

Generally, EOF is normal situation when you working with streams. Problem with EOF will rise only when one of JsonParser 's notice EOF in "the middle" of JSON object. When parser will read the whole object and will be satisfied there will be no problems. Since version 2.8 Jackson has JsonEOFException exception which precise when it will appear:

Specialized JsonParseException that is thrown when end-of-input is reached unexpectedly, either within token being decoded, or during skipping of intervening white-space that is not between root-level tokens (that is, is within JSON Object or JSON Array construct).

It is used in internal com.fasterxml.jackson.core.base.ParserMinimalBase parser class which is extended by many specific parsers such as UTF8StreamJsonParser . One from many methods which is used to handle EOF :

    protected void _reportInvalidEOF(String msg, JsonToken currToken) throws JsonParseException {
        throw new JsonEOFException(this, currToken, "Unexpected end-of-input"+msg);
    }